Prague, 8 April 2004 (RFE/RL) -- U.S.-led coalition forces in Iraq continued operations against Sunni and Shi'a insurgents today as the U.S. debates its troops strength in the country.

U.S. Marines pressed on with an operation to root out insurgents in the restive Sunni city of Al-Fallujah, west of Baghdad. Marines launched the operation after the deaths of four U.S. civilian security workers, who were killed and mutilated in the city last week.

U.S. Defense Secretary Donald Rumsfeld said the violence in Iraq is caused by a small number of people but that U.S. commanders are considering whether to send more forces into Iraq to help quell the surge in violence. He said some troops scheduled to leave soon may have to stay longer.

Rumsfeld acknowledged yesterday that U.S. troops face a "serious problem" with unrest in Iraq, but added that the United States remains in control of the situation and that American-led forces are on the offensive against the insurgents.

"The United States will stay the course. We will stay until the task is complete. As President [George W.] Bush has said, we did not charge hundreds of miles into the heart of Iraq and pay a bitter cost of casualties to liberate 25 million people, only to retreat before a band of thugs and assassins," Rumsfeld said.

He also said some nine suspects believed to have been involved in the civilian killings in Al-Fallujah have been arrested.

Reports say thousands of Sunni and Shi'a Muslims left Baghdad for Al-Fallujah today in cars full of food and medical supplies in a show of support for the residents of the besieged city.

Freelance translator Sami Alkhoja, who works for RFE/RL, reported from Baghdad this morning: "There are lots of trucks loading aid and food and people are donating money to be sent [to Fallujah]. They have already sent, in the morning...trucks into Fallujah with the Red Crescent to be delivered to the people of Fallujah -- medical supplies, food supplies."

AFP and AP, quoting local medical sources, say some 280 Iraqis have been killed in Al-Fallujah since the start of the operation.

Yesterday, Al-Fallujah's Abd al-Aziz al-Samarra'i Mosque was bombed by U.S. aircraft. The chief U.S. military spokesman in Iraq, General Mark Kimmitt, said Marines attacked the mosque only after it became clear enemy fighters were using it as a cover for attacks.

In the holy Shi'a city of Karbala, reports say Polish and Bulgarian troops today battled armed militiamen loyal to radical Shi'a cleric Muqtada al-Sadr, who control the city. The clashes in Karbala erupted as tens of thousands of pilgrims flocked to the city for a major Shi'a religious holiday. It is unclear whether there are casualties.

A Polish military spokesman told AFP that members of al-Sadr's Imam Al-Mahdi militia opened fire with rocket-propelled grenades and automatic weapons on Polish and Bulgarian soldiers protecting the governor's office in Karbala.

In Al-Najaf, south of Baghdad, AFP reported fighting between Spanish and Ecuadoran coalition forces and al-Sadr supporters. Al-Sadr is reported to have taken refuge in Al-Najaf.

In Baghdad, meanwhile, residents say U.S. forces today struck al-Sadr's office in his main stronghold, the sprawling Shi'a neighborhood of Sadr City. One Iraqi witness said: "The [U.S.] tanks came here and shelled [al-Sadr's] office. Then, at four o'clock in the morning, the helicopters came and hovered over the office and opened fire with their machine guns and then fired two missiles at the office."

The chairman of the Joint Chiefs of Staff, U.S. General Richard Myers, said the latest upsurge in fighting is not an uprising supported by Iraq's Shi'a majority. "I think it is also important to remember what this is not, and it is certainly not a popular uprising or a movement supported by the majority of Iraqis," he said. "It is not that at all."

News reports say fighting throughout Iraq this week has left 35 U.S. soldiers, one Ukrainian soldier, and at least 459 Iraqis dead.